Method for treating a water-containing waste oil

ABSTRACT

A method for treating a water-containing waste oil comprising oils, water and solid constituents and forming a water-in-oil emulsion, which comprises adding to the water-containing waste oil having an aromatic oil ratio A as represented by the following formula: ##EQU1## at least 1% by weight, on the basis of the weight of the water-containing waste oil, of a treating oil having an aromatic oil ratio B(|A-B|&gt;0.5 and excluding 0.4≦B≦0.6) thereby to separate the oil content.

TECHNICAL FIELD

This invention relates to a method for treating a water-containing waste oil, and more particularly to a method for treating a water-containing waste oil comprising oil, water and sludge contents and forming a water-in-oil emulsion, by admixing therewith a certain specific solvent.

BACKGROUND ART

At a coal tar plant, coal tar distillation gives distillates such as carbolic oil, naphthalene oil, wash oil and anthracene oil. When subjected to phenols(or acid)-extraction or base-extraction treatment or when used for recovery of light oil from coke over gas, such distillates are in contact with water and thereby yield a water-containing waste oil. Further, coal tar contains water in itself, and therefore, a waste oil likewise forms during its storage in a tank or at the time of its distillation. Furthermore, similar waste oils result from the washing of the tanks for various distillate oils.

Oil originated from coal tar have greater hydrophilic property than oils originated from petroleum, and accordingly they tend to form a water-in-oil emulsion. Depending on their origins, water-containing waste oils differ more or less from each other in their characteristics. However, they normally contain not only oil and water but also solid substance, i.e. sludge, and they form an extremely stable emulsion comprising these three components.

Water-containing waste oils collected from coal tar plants have a relatively uniform composition and they normally contain 10 to 40% by weight of oil, 1 to 5% by weight of sludge and the rest being water. The sludge contains inorganic substances mainly comprising iron compounds, resinous matters comprising aromatic condensed ring compounds, coke powder, coal powder, etc., and is swelled in a water-containing waste oil about ten times of the volume of its dried state. The oil fraction contains mainly benzene homologues as light distillates, naphthalenes as medium distillates and tricyclic aromatic compounds such as anthracenes as heavy distillates. The specific gravity of the oil fraction is relatively close to that of water and it varies depending upon the composition of the particular oil. The specific gravity becomes smaller than water as the proportion of light distillates increases or as the temperature rises.

Further, various petroleum-based water-containing waste oils are known such as rolling oil wastes, lubricating oil wastes, or wash oil wastes which result from the rolling or tube making operations at ironworks, or from the washing of a coke oven gas with a petroleum-type absorption oil, or from machine tool works; crude oil wastes, heavy oil wastes, residual oils from tanks, sludge oils resulting from washing of crude oil tanks or heavy oil tanks, or the production line of lubricating oils at petroleum refineries and petrochemical factories; lubricating oil wastes, automobile engine oil wastes, cutting oil wastes, anti-corrosive oil wastes from automobile industries, machine making factories and ship yards. Depending upon their origins, these petroleum-based water-containing waste oils differ more or less in their characteristics. However, they normally contain not only oil and water but also sludge as solid constituent, and they also contain additives such as emulsifiers. Thus, they form an extremely stable emulsion. For instance, waste oils derived from the rolling operation at a metal working plant, or from the washing operation of coke oven gas or from the machine tool works, are in a form of a water-in-oil emulsion (hereinafter referred to as W/O emulsion) comprising mixed oil which contains as principal constituent a petroleum-based oil such as a rolling oil, lubricating oil, machine oil or wash oil, water and fine solid particles such as iron oxides or carbon particles. Likewise, waste oils or sludge oils derived from the washing operation of the crude oil or heavy oil tanks at a petroleum refinery, or waste oils derived from the machine making factories or the like, are water-containing waste oils in a form of W/O emulsion.

These water-containing waste oils normally comprise at least 50% by weight of petroleum-based oil, 0.1 to 1.0% by weight of solid constituent (dry basis) and the rest being water. By a petroleum-based oil is meant an oil containing non-aromatic oil components as its principal constituents. The solid constituent comprises metal powders such as iron powder, iron compounds such as iron oxides, carbon particles, dusts or sands. In combination with water or oil, the solid content forms a sludge.

It is extremely difficult to treat such tar-based or petroleum-based water-containing waste oils for separation even by subjecting them directly to a centrifugal separator, as they are stable and undergo no substantial change with time in their original proportion of oil, emulsion, water and solid fractions. Further, the water-containing waste oils have poor combustibility and therefore they are inferior as fuels and they tend to block up the burner tip with sludge components.

It is known to add a certain surface active agent in order to recover oil components from tar-based water-containing waste oils (Japanese Unexamined Patent Publication No. 96,785/1976). However, this method is intended primarily to treat oil components heavier than water. Accordingly, when subjected to the centrifugal operation, while water can be separated satisfactorily, the separation of the sludge and oil can not be accomplished to a satisfactory degree. No satisfactory results are obtainable in such case where recovery of high quality oil is desired and where waste oils containing oil components lighter than water are treated.

There have been proposed various methods for treating petroleum-based emulsion type water-containing waste oils such as those mentioned above, for instance, a method wherein the waste oils are heated under pressure, and then cooled to separate the three phase of oil, water and solid, and each phase is centrifugally separated (Japanese Patent Publication No. 47,722/1976), a method wherein a waste oil is heated to demulsify the emulsion and after cooling, each layer is separated (Japanese Patent Publication No. 43,305/1976) or a method wherein a waste oil is centrifuged while being heated, whereby the sludge is separated from the oil and water, and the oil and water thus obtained are further centrifuged for separation (Japanese Unexamined Patent Publication 123,403/1977). These methods require great amounts of energy for heating, pressurizing and centrifuging and yet the separation of the oil and sludge is inadequate. Further, there has also been proposed a method wherein a light oil fraction is added to a sludge oil to extract the oil component and the extracted sludge oil thus obtained is heat treated or treated with a coagulant and then centrifugally separated into water and solid components (Japanese Patent Publication 15,025/1972), a method wherein a hydrocarbon solvent containing as its principal constituents propane, butane or a hydrocarbon mixture containing from propane to a light oil, is added to a waste oil or sludge thereby separating it into oil and sludge components (U.S. Pat. No. 3,684,699 and Japanese Unexamined Patent Publication No. 39,601/1974). However, these methods have drawbacks such that the operation is rather complicated or the separation of the oil and sludge components is inadequate. Further, it is known to add a coal tar neutral oil containing a small amount of a surface active agent dissolved therein to a sludge so as to disperse the sludge (U.S. Pat. No. 2,559,574). However, this method is not intended to separate the oil and water.

Accordingly an object of the present invention is to provide a novel method for treating a water-containing waste oil comprising oil, water and sludge and which is in a form of a water-in-oil emulsion.

Another object of the invention is to provide a method wherein a certain treating oil is added to a water-containing waste oil originated from coal tar or petroleum thereby to recover the oil components from the waste oil.

DISCLOSURE OF INVENTION

These objects may be accomplished by a method for treating a water-containing waste oil comprising oils, water and solid constituents and forming a water-in-oil emulsion, which comprises adding to the water-containing waste oil having an aromatic oil ratio A as defined by the following formula: ##EQU2## at least 1% by weight, on the basis of the weight of the water-containing waste oil, of a treating oil having an aromatic oil ratio B (|A-B|>0.5 and excluding 0.4≦B≦0.6) thereby separating the oil content.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing an influence, over the separation factor, of the amount of kerosene added against the amount of the oil content in the coal tar-based water-containing waste oil, and

FIG. 2 is a graph showing an influence, over the separation factor, of the solvent and a surfactant added against the coal tar-based water-containing waste oil.

BEST MODE OF CARRYING OUT THE INVENTION

The present inventors have found that it is possible to demulsify the above mentioned stable W/O emulsion and thereby to facilitate the precipitation of the sludge and its separation from water, by adding to a water-containing waste oil having an aromatic oil ratio A, i.e. a ratio of the weight of the aromatic oil content against the weight of the total oil content in the water-containing waste oil (hereinafter the aromatic oil ratio in the water-containing waste oil is simply called A) (preferably excluding the case where 0.4≦A≦0.6), at least 1% by weight, preferably 2 to 100% by weight and more preferably 5 to 50% by weight, on the basis of the weight of the water-containing waste oil, of a treating oil having an aromatic oil ratio B, i.e. a ratio of the weight of the aromatic oil content against the weight of the total oil content in the treating oil (hereinafter the aromatic oil ratio in the treating oil is simply called B) (|A-B|>0.5 and excluding a case where 0.4≦B≦0.6; preferably |A-B|>0.7 and excluding a case where 0.3≦B≦0.7). It is possible to separate the oil components simply by allowing the treated oil to stand still. Further it is possible to facilitate the separation of the sludge by means of a centrifugal separation. A mixture of oil and water thus obtained after separation of the sludge is allowed to stand still whereby the interface of the two phases becomes distinctive thus showing an improvement in the separation of oil and water.

The aromatic oils are oils comprising aromatic compounds such as benzenes, naphthalenes, biphenyls and anthracenes. As an example of the oil having a high aromatic oil content, a tar-based oil is mentioned, whereas as an example of the oil having a low aromatic oil content there is a petroleum-based oil which is normally available.

As typical aromatic oils, there may be mentioned, benzene, toluene, xylene, trimethylbenzene, tetramethylbenzene, ethylbenzene, styrene, cumene, naphthalene, methylnaphthalene, dimethylnaphthalene, biphenyl, anthracene, phenanthrene, indene, diphenylmethane, dibenzofuran, fluorene and the like. Where an aromatic ring is substituted by an alkyl or alkenyl group having a high number of carbon atoms such an aromatic compound tends to lose characteristics of the aromatic oil and to gain characteristics of the non-aromatic oil. Accordingly an aromatic compound having non-aromatic substituents such as an alkyl or alkenyl group having more than six carbon atoms should preferably be excluded from the calculation for the aromatic oil content.

Further, for the convenience for calculation of the aromatic oil content it is recommended to employ as a parameter the aromatic index obtained by the following calculation. For further details of this calculation, a reference may be made to Brennstoff Chemie 42,378 (1961).

    Aromatic index=C ar/C=1-(1/2)×(H/C)×(H.sub.al /H)

in this formula, C_(ar) /C is an atomic ratio of carbon atoms constitutional aromatic rings to the total carbon atoms, H/C is an aromatic ratio of hydrogen to carbon as obtained from an elementary analysis, and H_(al) /H is an atomic ratio of non-aromatic hydrogen atoms to all hydrogen atoms which is obtained from the following formula ##EQU3## (where, D_(ar) /D_(al) is an absorbance ratio of stretching vibration spectrum of C-H bonds, and is obtainable by absorbance of aromatic bond (3.3μ)/absorbance of aliphatic bond (3.42μ).

The aromatic factor thus obtained is useful as a reference for calculation of aromatic oil content. In particular, except in a case where peculiar oils such as a long chain alkybenzene or polyalkybenzene are involved, the aromatic factor can practically be used as the aromatic oil content in most cases.

Upon comparison of various kinds of treating oils to be added, it has been found that aromatic oils ranging from light oils such as benzene, toluene, and xylene to oils having high boiling points such as methylnaphthalene oil do not give adequate separation performance for coal tar-based water containing waste oils (A>0.5, preferably A>0.6). Whereas, oils derived from petroleum and containing 60% by weight or more, preferably 70% by weight or more of aliphatic hydrocarbons, which range from light oils such as hexane to oils having high boiling points such as fuel oil-C (according to Japanese Industrial Standard (hereinafter referred to JIS No. K2205), exhibit excellent separation performance. For instance, oils such as leadless gasoline containing 40% by weight or more of aromatic hydrocarbons are not suitable, whereas oils remaining after extraction of aromatic hydrocarbons from a cracked gasoline are useful. The treating oils must be liquid at room temperature.

The treating oils may differ in their separation performance more or less depending on their individual natures but provide sufficient performance for practical purposes. For use in practice, they may be selected taking into account such factors as manageability for handling, availability, and costs. From practical point of view, kerosene, light oil and fuel oil-A (according to JIS K 2205) as originated from petroleum are most suitable. Further, petroleum-based water-containing waste oil is likewise useful and economical and it is extremely advantageous to use this waste oil for treatment of other water-containing waste oil simply by admixing the waste oils. The amount of the treating oil to be used is determined taking into accouts the amounts of oil and sludge contents in the water-containing waste oil to be treated, and conditions for treatment and apparatus to be used for treatment. In general, however, if the difference between A of the water-containing waste oil and B of the treating oil is 0.8 or more, the amount of the treating oil per the amount of the water-containing oil (a ratio by weight) is at least 1% by weight, preferably 2 to 100% by weight and more preferably 5 to 50% by weight. Generally, when an additive such as a surface active agent is added, the amount to be used may be small, whereas when the difference between A and B is small, it is necessary to use a greater amount. Where the specific gravity of the oil content in the water-containing waste oil is greater than the specific gravity of water, the specific gravity of oil phase becomes greater than that of water, and it is necessary to add a solvent having a low specific gravity for adjustment. As far as the separation performance is concerned, there is no upper limit for the amount to be added, but it is not economical to use a greater amount.

On the other hand, various kinds of the treating oils have been compared for the treatment of petroleum-based water-containing waste oils (A<0.5, preferably A<0.4), and it has been found that aliphatic hydrocarbon oils ranging naphtha, kerosene, light oil and heavy oil, do not provide satisfactory separation performance with such petroleum-based water-containing waste oils.

Whereas, it has been found that aromatic oils containing at least 60% by weight, preferably 70% by weight or more, of aromatic hydrocarbons are useful as the treating oils for the petroleum-based water-containing waste oils. For example, there may be mentioned a light oil obtained by the absorption treatment of coke oven gas by an absorption oil, a light oil obtained by the fractional distillation of coal tar, a reformed oil obtained by aromatization of petroleum naphtha, crude or refined benzene, toluene or solvent naphtha obtained by the fractional distillation the reformed oil, or naphthalene oil, absorption oil, anthracene oil, creosote oil or a mixture thereof obtained from coal tar. Among these oils, aromatic oils mainly comprising distillates having a boiling point of 130° to 275° C. are particularly useful. Particularly, aromatic oils containing 20 to 60% of naphthalene is most useful. As an example of such aromatic oils, there may be mentioned a residual oil obtained by distillation of a tar light oil to remove the distillates up to xylene.

Further, a coal tar-based water-containing water-containing waste oil is also useful as the treating oil. For example, there may be mentioned waste oils obtained at coal tar plants by the phenols (or acid)-extraction or base extraction of coal tar distillates such as carbolic oil, naphthalene oil, wash oil or anthracene oil, and waste oils obtained by washing storage tanks for various oils.

The amount of the aromatic treating oils to be added is determined taking into account oil and sludge contents of the petroleum-based water-containing waste oil, the conditions for treatment, and the apparatus to be used for treatment. In general, however, if the difference between A of the water-containing waste oil and B of the treating oil is 0.8 or more, the amount of the treating oil per the amount of the water-containing waste oil (a ratio by weight) is at least 1% by weight, preferably 2 to 100% by weight or more preferably 5 to 50% by weight. Generally, when an additive such as a surfactant is added, the amount to be used may be smaller whereas when the difference between A and B is small, it is necessary to use a greater amount. As far as the separation performance is concerned, there is no upper limit for the amount to be added but it is not economical to use a greater amount.

The treatment of the water-containing waste oils by means of these treating oils is conducted at pH 4 to 8, preferably 6 to 7, whereby particularly good results are obtained.

Further, for the treatment of the coal tar-based water-containing waste oils, a favourable result is obtainable by using, in combination with the treating oil, a cationic surfactant containing a quaternary ammonium salt or an imidazole derivative as principal component. As such cationic surfactants, there may be mentioned an alkyl trimethylammonium salt, an alkyl hydroxyethyl imidazoline, an alkyl imidazoline acetate and an alkyl imidazoline salt. The cationic surfactants are added in an amount of 100 to 3,000 ppm, preferably 200 to 1,500 ppm, to the water-containing waste oils.

Further, for the treatment of the petroleum-based water-containing waste oils, anionic or non-ionic surfactants may advantageously be used together with the above mentioned treating oils whereby the amount of the treating oils to be added may considerably be reduced. As such anionic surfactants, there may be mentioned a fatty acid salt R₁ CH₂ COOM (where R₁ is an alkyl or alkenyl group having 11 to 17 carbon atoms, and M is Na or K), triethanolamine sulfonate or sodium sulfonate R₂ SO₃ Na (where R₂ is an alkyl group having 12 to 18 carbon atoms), ##STR1## (where R₃ is an alkyl group having 11 to 15 carbon atoms), ##STR2## (where R₄ is an alkyl group having 1 to 4 carbon atoms),R₅ CHCOOH (where R₅ is an alkyl group having 11 to 17 carbon SO₃ Na atoms), R₆ COOH₂ SO₃ Na (where R₆ is an alkyl group having 11 to 17 carbon atoms), ##STR3## (where R₇ is an alkyl group having 11 to 17 carbon atoms), ##STR4## (where R₈ and R₈ ' are alkyl group having a total of 10 to 20 carbon atoms), a lignin sulfonate, a higher alcohol, sulfuric ester salt R₉ OSO₃ Na (where R₉ is an alkyl group having 12 to 18 carbon atoms). ##STR5## (where R₁₀ and R₁₀ ' are alkyl groups having 12 to 18 carbon atoms), polyoxyethylene alkylether sulfate R₁₁ (CH₂ CH₂ O)_(n) SO₃ Na (where R₁₁ is an alkyl group having 8 to 18 carbon atoms, and n is an integer of 1 to 20), ##STR6## (where R₁₂ is an alkyl group having 8 to 18 carbon atoms, and m is an integer of 1 to 20), and an alkyl succinic ester. As nonionic surfactants, there may be mentioned a poly (oxyethylene)glycol alkylether R₁₃ --O(CH₂ CH₂ O)_(n) H (where R₁₃ is an alkyl group having 6 to 30 carbon atoms and n is an integer of 3 to 120), a poly(oxyethylene)alkyl arylether ##STR7## (where R₁₄ is an alkyl group having 6 to 12 carbon atoms and n is an integer of 3 to 120), a poly(oxyethylene)alkylester R₁₅ --COO(CH₂ CH₂ O)H or R₁₅ --COO(CH₂ CH₂ O)_(n-1) CH₂ CH₂ --COOR₁₅ (where R₁₅ is an alkyl group having (6 to 24 carbon atoms, and n is an integer of 3 to 120), a poly(oxyethylene)alkylamine R₁₆ --NH(CH₂ CH₂ O)_(n) H or ##STR8## (where R₁₆ is an alkyl group having 6 to 30 carbon atoms, and n and n' are integers of 1 to 120), a poly(oxyethylene)alkylamide R₁₇ --CONH(CH₂ CH₂ O)_(n) H or ##STR9## (where R₁₇ is an alkyl group having 6 to 30 carbon atoms, and n and n' are integers of 3 to 120), a poly(oxyethylene)sorbitan fatty acid ester ##STR10## (where R₁₈ is an alkyl group having 6 to 24 carbon atoms, and n is an integer of 3 to 60), a pluronic type poly(oxyethylene)poly(oxypropylene) copolycondensation product OH(CH₂ CH₂ O)_(a) (CH₃ CHCH₂ O)_(b) (CH₂ CH₂ O)_(c) H (where a, b and c>1 and (a+b+c)=20 to 400), and a Tetronic type copolycondensation product ##STR11## (where x to x"' and y to y"'>1, and x+X'+X"+X"'+y+y'+y"+y"'=20 to 800).

These surfactants may normally be added in an amount of 100 to 5,000 ppm, preferably 500 to 2,000 ppm based on the water-containing waste oil.

The above mentioned surfactants may be added as an aqueous solution of 1 to 10% if they are water soluble. If they are oil soluble, they may be added as they are or as dissolved in a petroleum-based or a coal tar-based treating oil.

After addition of an aliphatic or an aromatic treating oil and, if necessary, a surfactant, to the water-containing waste oil, it is necessary to agitate the mixture sufficiently to effect adequate admixing and contacting, and it is preferred to heat the mixture for this admixing operation. A suitable method of admixing may be employed such as pumping to circulate the mixture in a tank or mixing by means of line mixer. The heating should be conducted to give a temperature as high as possible within a limit that no problem is created the gasification of the waste oil or the solvent, practically 20° to 90° C. and preferably 50° to 70° C.

After the addition and admixing of the aliphatic or aromatic treating oil, the mixture is allowed to stand still whereby the oil components are separated. Further, after the addition and admixing of the aliphatic or aromatic treating oil, a sludge may be removed for instance by means of centrifugal separation, thereby facilitating the separation of the oil components. As a method for removing the sludge, the centrifugal method is most suitable. The greater the centrifugal force, the higher the separation efficiency becomes. However, the centrifugal force is normally at least 800 G and taking an economical aspect into consideration a preferred range is 2,000 to 4,000 G. It is preferred to carry out the separation of the sludge when applying this centrifugal force.

As apparatus for carrying out the sludge separation and oil-water separation simultaneously, various centrifugal separation apparatus may be used. Filtration apparatus are subject to a problem of blocking up of the filter if it is not surface replaceable type. With the surface replaceable type filter, it is then difficult to completely separate the sludge. For these reasons, the use of a centrifugal apparatus is preferred.

The filtration from which the sludge was removed by a centrifugal apparatus, is allowed to settle whereby it is separated into two phases, i.e. the upper oil layer and the lower water layer, with little emulsion layer left at the interface, and the oil layer and the water layer readily be separated and recovered, respectively.

The oil fraction thus recovered is at least useful as fuel. It may be used for more valuable purpose depending on the nature of the original waste oil from which it is recovered. On the other hand, the water layer contains only a dissolved amount of the oil and can readily be purified by activated sludge treatment without requiring any further pretreatment.

The method of the present invention will now be described in further detail with reference to the examples. The percentage used in the following examples is by weight unless otherwise specified.

EXAMPLES 1 TO 6 AND COMPARATIVE EXAMPLES 1 TO 3

A water-containing waste oil (a mixture of waste oils collected at a coal tar plant) containing 34.7% of an aromatic oil (A>0.9) which has a specific gravity and viscosity at 60° C. of 1.007 and 2.4 centipoise, respectively, and a H/C ratio (atomic ratio) of 1.015 and 2.3% of sludge (dry basis) and forming a water-in-oil emulsion, was used as the sample material.

A glass centrifuge tube graduated at 50 ml. was filled with 30 ml. of the sample material and 6 ml. of each treating oil, the mixture was agitated at 60° C. for 15 minutes and centrifuged at 1,500 G for 15 minutes with use of a centrifuge. The results as shown in Table 1 were obtained from the measurement of the oil layer, the water layer and the sludge layer which were separated in the centrifuge tube.

                  TABLE 1                                                          ______________________________________                                                              Water         Sludge                                                           re-     Oil re-                                                                              layer                                                            covery  covery                                                                               Pro-  Separ-                                                     factor  factor                                                                               portion                                                                              ation                                 Nos.   Treating oils (X)     (Y)   (Z)   factor                                ______________________________________                                         Exam-                                                                          ples                                                                           1      n-hexane (B = 0)                                                                             77      84    19    4.1                                   2      n-octane (B = 0)                                                                             90      82    11    7.8                                   3      kerosene (B < 0.1)                                                                           83      76    10    7.6                                   4      light oil (B < 0.1)                                                                          79      88    15    5.5                                   5      fuel oil-A (B < 0.1)                                                                         56      85    19    3.6                                   6      fuel oil-C (B < 0.1)                                                                         66      82    13    5.6                                   Compa-                                                                         rative                                                                         Exam-                                                                          ples                                                                           1      xylene (B = 1)                                                                               58      86    29    2.5                                   2      methylnaphthalene                                                                            19      48    68    0.5                                          (B = 1)                                                                 3      leadless gasoline                                                                            56      54    19    2.8                                          (B = 0.5)                                                               ______________________________________                                          Notes:                                                                         ##STR12##                                                                      ##STR13##                                                                      ##STR14##                                                                      ##STR15##                                                                     -   The water recovery factor and the oil recovery rate closer to 100           indicate better separation performance. The smaller the sludge layer      proportion is, the better the sludge is processed and the easier the      centrifugal separation of the sludge becomes. These relationships are      represented by a single equation of the separation factor which is found      to fairly well correspond to the actual separation efficiency. The greater      the separation factor is, the better the actual separation becomes.

It is apparent from Table 1 that when the difference between A and B is 0.5 or less, the separation efficiency is lower, particularly for the separation of the sludge, in the treating oil having a high aromatic compound content.

EXAMPLE 7

In a manner similar to Example 3, separation factors were obtained at various amounts of a kerosene used as the treating oil. The results, including Example 3 (0.6 ml. kerosene/ml. of oil in waste oil), are shown in FIG. 1.

EXAMPLE 8

2.6 m³ of kerosene was added to 10 m³ of the water-containing waste oil (A>0.9) originating from a tar plant and containing 26.7% of oil, 1.2% of sludge (dry basis) and the remainder of water, and the mixture was heated and agitated in a tank at 65° C. for 3 hours. This mixture was introduced to a centrifugal separator (Super Decanter) at a rate of 0.5 m³ /hr, and treated at 3,000 g for a residence time of 1.4 minutes, whereby the sludge and a liquid were continuously separated. The separated liquid fraction was allowed to stand still in a settling tank whereupon the oil fraction and the water fraction were recovered from the upper layer and the lower layer, respectively. The sludge thus obtained contained 27.1% of water and 47.8% of oil. The recovered oil fraction contained 0.3% of water and 0.06% of sludge. The separated water contained 66 ppm of oil and 22 ppm of suspended solids and was treated directly with the activated sludge treating apparatus.

EXAMPLES 9 TO 12

In a manner similar to Example 3, 30 ml. of the same sample material, 3 ml. of kerosene and 1,000 ppm of each of various surfactants were filled in a graduated glass centrifuge tube and the mixture was agitated at 60° C. for 30 minutes, and then centrifuged at 980 G for 15 minutes by means of a centrifuge. Water soluble surfactants were added as a 2% aqueous solution and oil soluble surfactants were added as a 2% kerosene solution. The results as shown in Table 2 were obtained from the measurements of the oil layer, the water layer and the sludge layer which were separated in the centrifuge tube.

                  TABLE 2                                                          ______________________________________                                                             Water    Oil                                                                   Separ-   Separ-                                                                               Sludge                                      Ex-                 ation    ation Pro-  Separ-                                am-                 Factor   Factor                                                                               portion                                                                              ation                                 ples Surfactant     (X)      (Y)   (Z)   Factor                                ______________________________________                                         9    Alkyl-         98.0     78.3  11.6  7.6                                        trimethylammonium                                                              salt                                                                      10   Alkylhydroxyethyl                                                                             97.9     78.3  12.1  7.3                                        imidazoline                                                               11   Alkyl imidazoline                                                                             102.9    76.9  8.7   10.3                                       acetate                                                                   12   Alkyl imidazoline                                                                             103.2    77.2  8.1   11.1                                       salt                                                                      ______________________________________                                          Notes:                                                                         Water Separation Factor (X)                                                    ##STR16##                                                                      Oil Separation Ratio (Y)                                                       ##STR17##                                                                      Sludge Proportion (Z)                                                          ##STR18##                                                                      ##STR19##                                                                

EXAMPLE 13

In a manner similar to Example 10, the relation between the separation factors and the amounts of the solvent and alkyl hydroxyethylimidazoline added was studied, with kerosene, fuel oil-A and fuel oil-C being used as the solvent. The centrifugal force was 1,250 G. The results are shown in FIG. 2. The curved lines in the FIG. represent the following:

    ______________________________________                                         Lines         Solvent   Surfactant (ppm)                                       ______________________________________                                         A             kerosene  2,000                                                  B             kerosene  1,000                                                  C             kerosene    500                                                  D             fuel oil-A                                                                               1,000                                                  E             Fuel oil-C                                                                               1,000                                                  ______________________________________                                    

EXAMPLES 14 AND 15 AND COMPARATIVE EXAMPLES 4 AND 5

A mixed waste oil from a metal working plant comprising petroleum oils such as rolling oils or machine oils as principal components and having a specific gravity at 4° C. of 0.842 and which contains 75% of oil (A<0.1) having elementary analysis values of C 85.3% and H 13.7%, 26% of water and 1.2% of solid components (dry basis) such as iron oxides and which is in a form of a water-in-oil emulsion, a treating oil and an additive were introduced into a centrifuge tube of 50 cc., and were then heated in a water bath at 60° C. for 30 minutes while being agitated from time to time. Then the mixture was subjected to a centrifuge separation at 1,250 G for 15 minutes by means of centrifuge. The centrifuge tube was withdrawn and the volumes of the oil layer, the intermediate layer (emulsion) between the oil layer and the water layer, the water layer and the precipitated layer (solid components plus water) were measured. The experimental results obtained for various kinds of the additives are shown in Table 3.

                                      TABLE 3                                      __________________________________________________________________________                           Volumes (ml) after centrifugal                                                                       Oil                                           Treating oils                                                                             separation            separa-                                   Waste                                                                              Additives               Precipi- tion                                      Oil       Amount                                                                              Oil                                                                               Intermedi-                                                                           Water                                                                              tated    factor                             Nos.   (ml)                                                                               Kinds (ml) layer                                                                             ate layer                                                                            layer                                                                              layer                                                                               Total                                                                              (%)                                __________________________________________________________________________     Example 14                                                                            30  Tar mixed                                                                            9    28 9.5   1   0.5  39  91                                            oil I                                                               Example 15                                                                            30  Tar mixed                                                                            9    29.5                                                                              0.5   7   2    39  95                                            oil I                                                                          Anionic                                                                              0.03                                                                     surfactant                                                          Comparative                                                                    Example 4                                                                             40  None  --   1  30    7   2    40  3                                  Comparative                                                                    Example 5                                                                             30  Kerosene                                                                             9    1  30    6   2    39  3                                  __________________________________________________________________________      Note 1.                                                                        Tar mixed oil I: a tarbased light oil distillation residue (B > 0.9)           consisting mainly of xylene, trimethylbenzene, naphthalene,                    methylnaphthalene and having a boiling point of about 140 to 230°       C.                                                                             Note 2.                                                                        Anionic surfactant: dioctyl sodium sulfosuccinate                              Note 3.                                                                        ##STR20##                                                                

EXAMPLES 16 to 25 AND COMPARATIVE EXAMPLES 6 TO 7

A mixed waste oil (A-0.2) from an ironworks containing petroleum oils such as lubricant oils, and wash oils for coke oven gas, as principal components, and having a specific gravity at 4° C. of 0.835 and which contains 55% of oil having elementary analysis values of C 85.5% and H 13.2%, 44% of water and 1.5% of solid content (dry basis) such as carbon particles and which is in a form of an emulsion, was admixed with a treating oil and an additive. The mixture was subjected to the centrifuge experiments in a manner similar to Examples 14 and 15. The results thereby obtained are shown in Table 4.

                                      TABLE 4                                      __________________________________________________________________________                             Volumes (ml) after centrifugal                                                                       Oil                                         Treating oils,                                                                              separation            separa-                                 Waste                                                                              Additives                 Precipi- tion                                    oil         Amounts                                                                             Oil                                                                               Intermedi-                                                                           Water                                                                              tated    factor                           Nos.   (ml)                                                                               Kinds   (ml) layer                                                                             ate layer                                                                            layer                                                                              layer                                                                               Total                                                                              (%)                              __________________________________________________________________________     Example 16                                                                            30  Grade 5 15   29 3.5   10.5                                                                               2    45  92                                          Xylene (B = 1)                                                      Example 17                                                                            30  Grade 5 15   32 trace 8   5    45  100                                         Xylene  2000 ppm                                                               Anionic                                                                        surfactant                                                          Example 18                                                                            30  Methyl- 6    21 3     10  2    36  98                                          naphthalene                                                                    (B = 1)                                                             Example 19                                                                            30  Methyl- 6    22 trace 9.5 4.5  36  100                                         naphthalene                                                                            2000 ppm                                                               Anionic                                                                        surfactant                                                          Example 20                                                                            30  Coal tar                                                                               6    21.5                                                                              1.5   11  2    36  100                                         absorption                                                                     oil (B > 0.9)                                                       Example 21                                                                            30  Coal tar                                                                               6    22 trace 10  4    36  100                                         absorption                                                                     oil                                                                            Anionic                                                                        surfactant                                                          Example 22                                                                            30  Tar mixed                                                                              6    21.5                                                                              1.5   10  3    36  100                                         Oil I                                                               Example 23                                                                            30  Tar mixed                                                                              6    23 trace 8   5    36  100                                         Oil I   2000 ppm                                                    Example 24                                                                            30  Aromatic                                                                               15   29 3     11  2    45  92                                          solvent                                                                        naphtha                                                                        (B > 0.9)                                                           Example 25                                                                            30  Aromatic                                                                               15   31 trace 9   5    45  98                                          solvent                                                                        naphtha 2000 ppm                                                               Anionic                                                                        surfactant                                                          Comparative                                                                    Example 6                                                                             30  Kerosene                                                                               15   27 4.5   10  3.5  45  86                               Comparative                                                                    Example 7                                                                             35  None    --   16 4     12  3    35  83                               __________________________________________________________________________      Note 1.                                                                        Coal tar absorption oil: Distillate fraction having a boiling point of         250° C. to 300° C. in the vicinity of dimethyl naphthalene       to anthracene.                                                                 Note 2.                                                                        Anionic surfactant: dioctyl sodium sulfosuccinate.                       

EXAMPLE 26

To a waste oil from an ironworks having the same composition as the one in Example 16, 20% by volume of the tar mixed oil I of Example 14 and 2,000 ppm of dioctyl sodium sulfosuccinate were added, and the mixed liquid was agitated at 70° C. for 30 minutes. Then, the liquid was subjected to filtration under a reduced pressure of 250 to 300 mm Hg by means of 11 G 3 glass filter. After 150 minutes, the filtration was still possible. The filtrate obtained by 150 minutes was 73 ml. The filtrate was readily separated to an oil layer and a water layer.

COMPARATIVE EXAMPLE 8

The procedure of Example 26 was followed without addition of the tar mixed oil I. After about 60 minutes, the filtration became impossible due to blocking up of the filter. The filtrate obtained by this time was 20 ml.

EXAMPLE 27 AND COMPARATIVE EXAMPLE 9

To 20 ml of a crude oil tank sludge comprising 88.6% by volume of waxy material (A-0.1), 7% by volume of water, and 4.4% by volume of solid content (dry basis) and having a specific gravity of about 0.9, 20 ml of the tar mixed oil I of Example 14 or kerosene was added and heated at a temperature of 80° C., and the procedure of Example 14 was followed under the same conditions for heat mixing and centrifugal separation, whereby the results as shown in Table 5 were obtained.

                  TABLE 5                                                          ______________________________________                                                 Volumes (ml) after centrifugal                                                 separation                                                                                  Inter-      Pre-       Oil sepa-                                               medi-       cipi-      ration                                   Treat-  Oil    ate   Water tated      factor                             Nos.  ing oils                                                                               layer  layer layer layer                                                                               Total (%)                                ______________________________________                                         Ex-   Tar     33.5   0.5   2     4    40    89                                 ample mixed                                                                    27    oil 1                                                                    Com-  Kero-   24     12    --    4    40    64                                 para- sene                                                                     tive                                                                           Ex-                                                                            ample                                                                          ______________________________________                                    

Further, a similar experiment was carried out without using the treating oil, whereby no separation of the emulsion occurred.

EXAMPLES 28 TO 33

To a waste oil from an ironworks similar to the one used in Example 14, 30% of a residual oil (B-0.9) (boiling point of about 140° to 230° C.) which was obtained by distillation of tar-based light oil whereby distillates up to xylene were removed, and a surfactant were added and mixed. The mixture was heated at 70° C. for 30 minutes, and then subjected to the centrifugal separation at 1250 G for 15 minutes. The results are shown in Table 6.

                                      TABLE 6                                      __________________________________________________________________________                            Volumes (ml) after centrifugal separation               Surfactants            Oil                                                                               Intermediate                                                                          Water                                         Examples  Kind    Amount                                                                              layer                                                                             layer  layer                                                                              Precipitation                             __________________________________________________________________________     28   Amionic                                                                             Triethanol-                                                                            1000 ppm                                                                            30.0                                                                              2.0    6.5 0.5                                                 amine                                                                          dodecyl-                                                                       benzenesul-                                                                    fonate                                                               29        Dioctyl 1000 29.5                                                                              0.5    7.0 2.0                                                 sodium                                                                         sulfosuc-                                                                      cinate                                                               30        Succinic                                                                               1000 25.5                                                                              5.5    7.5 0.5                                                 acid                                                                           ester                                                                31        Sodium  1000 23.5                                                                              7.0    7.0 1.5                                                 dodecyl-                                                                       benzene-                                                                       sulfonate                                                            32   Nonionic                                                                            Ethyleneoxide-                                                                         1000 18.0                                                                              15     4.5 1.5                                                 propyleneoxide                                                                 copolymer                                                            33        Sorbitan                                                                               1000 15.0                                                                              18.5   4.0 1.5                                                 mono-                                                                          palmitate                                                            __________________________________________________________________________

EXAMPLE 34

0.02 part of a residual oil (boiling point of 140 to 230° C.) obtained by the distillation of tar light oil to remove the distillates up to xylene, and 2,000 ppm of triethanolamine sodium dodecylbenzenesulfonate, were added to 1 part of an automobile engine oil waste (composition measured by a centrifugal separation method: 91.7% by volume of oil (A<0.1), 3.8% by volume of water and 4.5% by weight of precipitation). The mixture was heated and agitated and then subjected to the centrifugal separation experiments.

As the results, 0.91 part of oil, 0.04 part of water and 0.007 part of the precipitation were recovered.

Further, when the mixture was heated at 80° C. for 2 hours and kept to stand still, slightly more than 0.7 volume of a clear oil layer appeared as the upper layer. When the mixture was further kept to stand still at a room temperature for 24 hours, the volume of the oil layer became slightly more than 0.8 volume.

When the waste oil alone was heated at 80° C. and kept to stand still, there appeared no change even after two hours.

EXAMPLES 35 TO 39 AND COMPARATIVE EXAMPLES 10 AND 11

A mixed waste oil from an ironworks containing petroleum oils such as rolling oils or machine oils as principal components and having a specific gravity at 4° C. of 0.842 and which contains 73% of oil (A<0.2) having elementary analysis values of C 85.3% and H 13.7% and which is in a form of a water-in-oil emulsion, and a tar-based water-containing waste oil were introduced in predetermined amounts into a centrifuge tube of 50 cc, and were then heated in a water bath at 60° C. for 30 minutes while being agitated from time to time. The mixture was subjected to a centrifugal separation at 1,250 G for 15 minutes by a centrifuge. The centrifuge tube was withdrawn and the volumes of the oil layer, the intermediate layer (emulsion) between the oil layer and the water layer, the water layer and the precipitated layer (solid content plus water) were measured. The experimental results are shown in Table 7.

                                      TABLE 7                                      __________________________________________________________________________                             Volumes (ml) after centrifugal                                   Tar-based water                                                                              separation                                                   Waste                                                                              containing       Intermediate      Oil                                     oil waste oil, or                                                                           Amount                                                                              Oil                                                                               layer  Water                                                                              Precipitated                                                                          separation                        Nos.  (ml)                                                                               additives                                                                               (ml) layer                                                                             (emulsion)                                                                            layer                                                                              layer  factor (%)                        __________________________________________________________________________         35                                                                               30  Water-containing                                                                        12   24 2      11.5                                                                               4.5    90                                          waste oil from                                                                 a tar plant                                                              36                                                                               30  Water-containing                                                                        12   24.5                                                                              1.5    12.0                                                                               4      92                                          waste oil from a                                                               tar plant                                                                      Anionic surfactant                                                   Exam-                                                                              37                                                                               30  Water-containing                                                                        12   25 1      12.0                                                                               4      94                                ples      waste oil from a                                                               tar plant                                                                      Nonionic                                                                       surfactant                                                               38                                                                               12  Water-containing                                                                        30   18 2      17  5      86                                          waste oil from                                                                 a tar plant                                                              39                                                                               12  Water-containing                                                                        30   20.5                                                                              1      15.5                                                                               5      98                                          waste oil from a                                                               tar plant                                                                      Cationic                                                                       surfactant                                                           Comp.                                                                              10                                                                               40  None      --  1  30     7   2      3                                 Exam-                                                                          ples                                                                               11                                                                               30  Kerosene 9    1  30     6   2      3                                 __________________________________________________________________________      Note 1.                                                                        Water-containing waste oil from a tar plant: Watercontaining waste oil         having a specific gravity and visocity at 60° C. of 1.007 and 2.4       c.p., respectively and containing 34.7% of oil having a H/C factor (atomi      ratio) of 1.015 and 2.3% of solid content (dry basis) (Collected from a        coal tar plant) (B > 0.8)                                                      Note 2.                                                                        Anionic surfactant: Dioctyl sodium sulfosuccinate ester                        Nonionic surfactant: Ethylene oxidepropylene oxide copolymer                   Cationic surfactant: Alkylhydroxyethyl imidazoline 1,000 ppm of each was       added.                                                                         Note 3.                                                                        ##STR21##                                                                

EXAMPLE 40

A water-containing waste oil D (90.1% of oil (A<0.1), 5.4% of water and 4.5% of solid content) originated from a lublicant oil and containing petroleum oils as principal constituents and a water-containing waste oil E (82% of oil (B>0.8) (tar-based heavy oils having a boiling point higher than 200° C. constitute the principal components), 15% of water and 3% of solid content) were mixed to separate the oil components. (1) The mixture of the waste oils D and E was kept at 70° C. for 2 hours.

    ______________________________________                                         Waste oil D (ml)                                                                          Waste oil E (ml)                                                                             Separated Oil layer (ml)                              ______________________________________                                         0          20            0                                                     1          19            14                                                    10         10            15.5                                                  19         1             16.5                                                  20         0             0                                                     ______________________________________                                    

(2) The mixture of the waste oils D and E was centrifuged at 1,250 G for 15 minutes and then kept to stand still for a short period of time for separation of oil components.

    ______________________________________                                         Waste   Waste     Separated  Water                                             oil D   oil E     oil layer  layer   Sludge                                    (ml)    (ml)      (ml)       (ml)    (ml)                                      ______________________________________                                         0       20        0          0       1.0                                       10      10        16.5       1.5     1.5                                       20      0         0          0       1.5                                       ______________________________________                                    

(3) The mixture of the waste oils D and E with added surfactant was centrifuged at 1,250 G for 15 minutes and subjected to the oil-water separation.

    ______________________________________                                                                 Separa-                                                Waste Waste             ted oil      Water                                     Oil D oil E   Surfactant                                                                               layer Emulsion                                                                              layer Sludge                              (ml)  (ml)    (ppm)     (ml)  (ml)   (ml)  (ml)                                ______________________________________                                          0    20      Cationic  9.2   9.0    0.0   1.8                                               1,000                                                            10    10      Cationic  17.0  0      1.6   1.4                                               1,000                                                            20     0      Anion     14.2  1.0    2.7   2.1                                 ______________________________________                                          Note 1. Cationic: Imidazoline type cation surfactant                           Note 2. Anionic: Alkyl sodium sulfosuccinate ester                       

INDUSTRIAL APPLICABILITY

As described hereinabove, the method of the present invention for the treatment of a water-containing waste oil is useful for treating tar-based water-containing waste oils discharged from coal tar plants or petroleum-based water-containing waste oils, originated from the rolling or tube making processes at ironworks or from the process of washing crude oil tanks or heavy oil tanks at petroleum refineries and petrochemical plants or derived from crude oil wastes, heavy oil wastes or residual oils in tanks. 

What is claimed is:
 1. A method for treating a water-containing waste oil comprising oils, water, and solid constituents in which the water is present in a water-in-oil emulsion, which comprises adding to the water-containing waste oil having an aromatic oil ratio A at least 1% by weight, on the basis of the weight of the water-containing waste oil, of a treating oil having an aromatic oil ratio B in which the values of the aromatic oil ratios, A and B, are determined by the following formula: ##EQU4## and in which, when A is greater than 0.5, B is less than 0.4 and, when A is less than 0.5, B is greater than 0.6, whereby in the water-containing waste oil and treating oil mixture the oil content is separated from the water and the solid constituents, and recovering the separated oil.
 2. A method as claimed in claim 1, wherein the amount of the treating oil added to the water-containing waste oil is 2 to 100% by weight.
 3. A method as claimed in claim 2, wherein the amount of the treating oil added to the water-containing waste oil is 5 to 50% by weight.
 4. A method as claimed in claim 1, wherein the aromatic oil ratio A of the water-containing waste oil minus the aromatic oil ratio B of the treating oil is greater than 0.7.
 5. A method as claimed in claim 1, wherein the addition of the treating oil is followed by removal of the solid content by means of a centrifugal force and then by separation of oil and water by means of a standing still separation.
 6. A method as claimed in claim 5, wherein the centrifugal force is at least 800 G.
 7. A method as claimed in claim 1, wherein the addition and mixing of the treating oil are conducted at a temperature of 20° to 90° C.
 8. A method as claimed in claim 7, wherein the addition and mixing of the treating oil are conducted at a temperature of 50° to 70° C.
 9. A method as claimed in claim 1, wherein the aromatic oil ratio of the water-containing waste oil is A<0.4 or A>0.6.
 10. A method as claimed in claim 9, wherein the water-containing waste oil has an aromatic oil ratio of A>0.6 and is a water containing waste oil derived from coal tar.
 11. A method as claimed in claim 10, wherein the treating oil has an aromatic oil ratio of B<0.4 and is an aliphatic oil derived from petroleum.
 12. A method as claimed in claim 11, wherein the aliphatic oil is selected from a group consisting of kerosene, light oil and fuel oil-A.
 13. A method as claimed in claim 10, wherein along with treating oil, a cationic surfactant containing a quaternary ammonium salt or imidazole derivative as the principal component is added in an amount of 100 to 3,000 ppm to the water-containing waste oil.
 14. A method as claimed in claim 9, wherein the water-containing waste oil has an aromatic oil ratio of A<0.4 and is a water-containing waste oil derived from petroleum.
 15. A method as claimed in claim 14, wherein the treating oil has an aromatic oil rato of B>0.6 and is an aromatic oil derived from coal tar.
 16. A method as claimed in claim 15, wherein the aromatic oil contains distillates having a boiling point of 130° to 275° C., as principal constituents.
 17. A method as claimed in claim 16, wherein the aromatic oil contains 20 to 60% by weight of naphthalene.
 18. A method as claimed in claim 16, wherein the aromatic oil is a residual oil obtained by distillation of a light oil to remove distillates up to xylene, said light oil being obtained either by distillation of coal tar or by collection from a coke oven gas.
 19. A method as claimed in claim 14, wherein along with the treating oil, an anionic or nonionic surfactant is added in an amount of 100 to 5,000 ppm to the water-containing waste oil.
 20. A method as claimed in claim 1, wherein pH of the mixture is 4 to
 8. 21. A method as claimed in claim 20, wherein pH of the mixture is 6 to
 7. 